Method and apparatus for drying free flowing material



Sept. 5, 1967 N. T. GRAY 3,339,287

METHOD AND APPARATUS FOR DRYING FREE FLOWING MATERIAL Filed Aug. 16, 1965 I 2 Sheets-Sheet l INVENTOR.

Norman T Gray Attorneys Sept. 5, N. T. GRAY METHOD AND APPARATUS FUR DRYING FREE FLOWING MATERIAL Filed Aug. 16, 1965 V 2 Sheets-Sheet 2 FI'g Z Z4 6 Z4 INVENTOR.

Norman T Gray Fig. 4

Attorneys United States Patent This invention relates to a method and apparatus for drying free flowing material, and in particular to a continuous dryer of the gravity type, and to a manner of constructing such a dryer.

Heretofore, there have been known gravity dryers consisting of a plurality of horizontal beds in vertical arrangement, the material to be dried being moved from the uppermost bed to the lowermost as by passing through a plurality of spaced holes provided in each bed. To prevent uneven material flow patterns, there have been employed rotating plows or shakers to help move the ma terial being dried and for maintaining proper flow of material through the dryer. Such mechanisms contribute substantially to the cost of manufacture and complexity of the dryer.

Furthermore, in counterflow operation, the same drying air flows successively through each bed of material from the output to the input. Thus, air reaching material in any bed contains moisture which it has acquired from previous material. Since the drying rate is a direct function of the difference of humidity of air saturated with water, and that of the air being applied, it is seen that the increased moisture in the drying air at each bed slows down the drying rate for that bed compared to what it would have been if fresh air had been used. There is, therefore, a need for an improved dryer.

Accordingly, it is an object of the present invention to provide an improved method and apparatus for drying free flowing material and construction therefor which will overcome the above named disadvantages.

Another object of the invention is to provide a method and apparatus of the above character in which moisture laden drying gases are channeled away from the material being dried at each level or bed, thereby eliminating moisture contamination of incoming material.

Another object of the invention is to provide a method and apparatus of the above character in which the material being dried and the drying gases and moisture travel in different channels so that moist air from one bed does flow into other beds.

Another object of the invention is to provide a method and apparatus of the above character in which the materialflows evenly through the apparatus under gravity without the need for mechanical mechanisms for helping to drive the material.

Another object of the invention is to provide a method and apparatus of the above character in which the material being dried does not form pockets of accumulated material.

' Another object of the invention is to provide a method and apparatus of the above character which takes the form of an array of cells, each cell performing material flow control, drying gas flow control, and heating functions.

Another object of the invention is to provide a method and apparatus of the above character in which a plurality of heating elements are distributed uniformly throughout the entire apparatus.

Another object of the invention is to provide a dryer of the above character which can be constructed of inexpensive folded sheet metal material.

These and other objects and features of the invention will be apparent from the following description when taken together with the accompanying drawings of which:

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FIGURE 1 is a side elevation view, partly in section, of drying apparatus constructed according to the invention in a typical installation.

FIGURE 2 is a perspective view of the drying vessel of FIGURE 1.

FIGURE 3 is a cross-section view of the drying vessel of FIGURE 2 taken along the lines 3-.3.

FIGURE 4 is a cross-sectional view of the dryer of FIGURE 2 taken along the lines 4-4 of FIGURE 2.

FIGURE 5 is a partially exploded isometric view showing one method of making a drying apparatus of the invention.

FIGURE 6 is a view showing the sheet before stamping.

Referring to FIGURES 1-4, the drying apparatus of the invention generally comprises a drying vessel 10 disposed in material receiving relation to a feed hopper 12. One side 14 of the vessel 10 is connected to an input plenum 16 laded by a perforated plate or screen-like member 17 for evenly supplying drying gas under pressure developed by blower 18. The other side 20 is connected to an output plenum 22 for discharging gases that have passed through the vessel 10. Dried material is discharged from the lowermost portion of the vessel 10 onto suitable receiving means such as a conveyor belt diagrammatically indicated at 23.

The drying vessel 10 comprises an array of horizontally extending cells 24. Each cell 24 is bounded by four walls which are arranged to form a generally prismatic diamond-like pattern in which the edges between the walls lie at the top, bottom, and sides of each cell. The two adjacent walls lying uppermost form a gas retaining crest or channel 25 along their lower surfaces 26 and 28. The opposite walls, lying lowermost, provide a material supporting trough 30 along their upper surfaces 31 and 32, and are spaced apart at their lower margins 34 and 36 for discharging material which has passed through the cell. The lower margins 34 and 36 lie at the side edges of the cells of a next tier therebelow to thereby serve to admit the material to be dried into the latter cells.

More specifically, the cells are arranged in a repeated two-dimensioned array, each cell 24 being generally diamond shaped in section (FIGURE 2). The array is composed of a plurality of levels or tiers (A-G), adjacent tiers being offset the half width of a cell so that the cells of one tier have walls in common with the next adjacent tier. Thus, each of the interior walls 37 and 38 within the apparatus provides an operative surface in each of two adjacent cells, each wall 37 being connected at the upper margin thereof to the next adjacent wall 38 to form an upside-down V-shaped channel for collecting vapor and for controlling the flow of gases through the cell. The walls 37 and 38 form material supporting surfaces 31 and 32 inclined to the horizontal so that the material distributed to the upper surfaces 31 and 32 slides downwardly across them from their upper margins 39 and 40 to their lower margins 34 and 36 as indicated by the arrows in FIGURE 2. The material then flows over the connected upper margins 39 and 40 of the upper surfaces 31 and 32 of the walls of the next tier therebelow for continued movement in the same manner therealong.

The walls are inclined to the horizontal at an angle greater than the angle of repose for the material to be dried so that the material flows through the dryer freely under gravity. The walls are constructed of any heat conductive metal material possessing sufiicient abrasion resistance to insure a reasonable lifetime. Stainless steel or strong aluminum alloy sheet are preferred materials. Heaters are provided for heating the materials flowing through each cell and consists of heating elements 41 disposed longitudinally and cent-rally within each of the cells 24.'The heating elements can take any of various forms such as electric heaters or gas burners, but preferably electric resistance heaters (Calrod) are employed. The electric heaters are connected to a suitable electrical power source 42 through conductors 43. Each heating element 41 operates to heat not only the material being dried in the cell in which it is disposed and flowing under it, but also the under side of the walls above it, to thereby contribute to the heating of material flowing through the overlying tier. Thus, material flowing through a cell is both directly heated by the heater (radiation and convection) and indirectly heated by conduction through the walls supporting the material.

In FIGURES 5 and 6, one manner of constructing a dryer of the invention is shown. A plurality of rectangular sheets 50 of metal are stamped to provide spaced apart parallel slots 52 therealong which are parallel to one side of the sheet 50. The slots are spaced from the other side of each sheet to leave a small portion 54 of material next to the ends of the slots for supporting the sheet as one piece. The sheets 50 are then folded over the slots and along bend lines 56 (at the slots) and 58 (running parallel and midway between the slots) to form an alternating or corrugated pattern in cross section. The pattern is characterized by slots at each trough and by upwardly closed channels at the crests. A plurality of sheets are arranged so that as a second sheet is placed over a first sheet, the troughs or lower portions of the second sheet lie juxtaposed the crests or top portion of the first to form a diamond shaped pattern of cells. It is also seen that the slots of the second sheet lie over the channels or uppermost part of the material supporting surfaces of the lower sheet.

The sheets may be held together by any suitable means. In the example shown, they are made in a self-supporting unit by fastening or welding the portions 54 adjacent the slots of one sheet to the next lower sheet.

By way of illustration, a dryer of the following specifications was constructed for drying sand.

(at) Slot width A".

(b) Distance between slots before bending 4". (c) Width (along line 58) 18". (d) Material of construction Stainless steel. (e) Heaters Calrod electric resistance.

It is apparent from the foregoing that I have provided a method and apparatus for drying material which posess several advantages compared with prior art structures. The dryer of the invention operates to maintain a separation of flow between the drying gases and the material being dried, thereby eliminating moisture contamination of incoming material. Furthermore, the invention provides a simple structure which is easily built and which is adapted for construction in a variety of sizes, depending upon the needs of the user. In this connection, it will be observed that the several sheets utilized in one embodiment of the invention are capable of being preformed into their corrugated pattern, and packaged and stacked together so that the crests and troughs coincide to thereby make a compact, easily shippable package.

I claim:

1. In apparatus for drying particulate material, an

enclosed vessel, means forming an input plenum connected to one side of said vessel for supplying drying gas to the interior thereof, means forming an output plenum connected to the horizontally opposite side of said vessel for discharging drying gases that have passed through the vessel, a plurality of material supporting metal sheets, mounting means supporting said sheets in a two dimensional array to form elongate cells extending horizontally in parallel alignment between the input plenum and output plenum within said vessel, said plurality of metal sheets being constructed and arranged and in connected pairs joined together at their upper margins at an angle and extending downwardly and outwardly therefrom, each of said sheets being disposed at an equal angle to the horizontal which is greater than the angle of repose for the material to be dried, said mounting means supporting the pairs of sheets in tiers having a plurality of adjacent pairs in each tier, the lower margins of each adjacent pair within a tier being spaced apart to form a material passageway, the upper margins of the connected pairs of a given tier lying immediately beneath and in a material receiving relationship to the material passageways provided in the tier immediately thereabove so that material delivered to the uppermost tier slides down the sheets thereof in free movement under gravity flow for predetermined distance and is discharged through the material passageways of said tier to the upper margins of the sheets of the tier next below which divert the stream of material for free movement under gravity flow along the upper surfaces of the sheets of said second tier, said material flowing in like manner downwardly through the tiers to the lowermost portion of the vessel, the material being subjected to the action of the drying gases flowing through the vessel from the inlet plenum to the outlet plenum.

2. Apparatus as in claim 1 in which the plurality of pairs of material supporting surfaces of each tier are formed in a unitary structure comprising a metal sheet having a corrugated conformation with slots at the troughs and closed at the crests, the sheets being mounted in horizontal planes so that the slots of one sheet overlie the troughs of the next lower sheet.

3. Apparatus as in claim 1 further including means for heating the material being dried as it flows through the vessel including a plurality of elongate heating elements, each of said heating elements being disposed in one of said cells, said heating elements serving to heat the lower surfaces of the upper pair of sheets thereabove which by conduction directly heats material flowing over the upper surfaces of such sheets, said heating element also serving to heat the upper surfaces and any material flowing therealong of the sheets below said element.

4. Apparatus as in claim 3 wherein said heating elements are electrical resistance rods.

KENNETH W. SPRAGUE, Primary Examiner. 

1. IN APPARATUS FOR DRYING PARTICULATE MATERIAL, AN ENCLOSED VESSEL, MEANS FORMING AN INPUT PLENUM CONNECTED TO ONE SIDE OF SAID VESSEL FOR SUPPLYING DRYING GAS TO THE INTERIOR THEREOF, MEANS FORMING AN OUTPUT PLENUM CONNECTED TO THE HORIZONTALLY OPPOSITE SIDE OF SAID VESSEL FOR DISCHARGING DRYING GASES THAT HAVE PASSED THROUGH THE VESSEL, A PLURALITY OF MATERIAL SUPPORTING METAL SHEETS, MOUNTING MEANS SUPPORTING SAID SHEETS IN TWO DIMENSIONAL ARRAY TO FORM ELONGATED CELLS EXTENDING HORIZONTALLY IN PARALLEL ALIGNMENT BETWEEN THE INPUT PLENUM AND OUTPUT PLENUM WITHIN SAID VESSEL, SAID PLURALITY OF METAL SHEETS BEING CONSTRUCTED AND ARRANGED AND IN CONNECTED PAIRS JOINED TOGETHER AT THEIR UPPER MARGINS AT AN ANGLE AND EXTENDING DOWNWARDLY AND OUTWARDLY THEREFROM, EACH OF SAID SHEETS BEING DISPOSED AT AN EQUAL ANGLE TO THE HORIZONTAL WHICH IS GREATER THAN THE ANGLE OF REPOSE FOR THE MATERIAL TO BE DRIED, SAID MOUNTING MEANS SUPPORTING THE PAIRS OF SHEETS IN TIERS HAVING A PLURALITY OF ADJACENT PAIRS IN EACH TIER, THE LOWER MARGINS OF EACH ADJACENT PAIR WITHIN A TIER BEING SPACED APART TO FORM A MATERIAL PASSAGEWAY, THE UPPER MARGINS OF THE CONNECTED PAIRS OF A GIVEN TIER LYING IMMEDIATELY BENEATH AND IN A MATERIAL RECEIVING RELATIONSHIP TO THE MATERIAL PASSAGEWAYS PROVIDED IN THE TIER IMMEDIATELY THEREABOVE SO THAT MATERIAL DELIVERED TO THE UPPERMOST TIER SLIDES DOWN THE SHEETS THEREOF IN FREE MOVEMENT UNDER GRAVITY FLOW FOR PREDETERMINED DISTANCE AND IS DISCHARGED THROUGH THE MATERIAL PASSAGEWAYS OF SAID TIER TO THE UPPER MARGINS OF THE SHEETS OF THE TIER NEXT BELOW WHICH DIVERT THE STREAM OF MATERIAL FOR FREE MOVEMENT UNDER GRAVITY FLOW ALONG THE UPPER SURFACES OF THE SHEETS OF SAID SECOND TIER, SAID MATERIAL FLOWING IN LIKE MANNER DOWNWARDLY THROUGH THE TIERS TO THE LOWERMOST PORTION OF THE VESSEL, THE MATERIAL BEING SUBJECTED TO THE ACTION OF THE DRYING GASES FLOWING THROUGH THE VESSEL FROM THE INLET PLENUM TO THE OUTLET PLENUM. 